III/V semiconductor lasers have an important technological role (e.g., in optical fiber communications, medical equipment, CD players), and further growth of the use of such lasers can be confidently anticipated.
In view of the wide use of III/V semiconductor lasers, it would clearly be highly advantageous to be able to manufacture the lasers with high yield, since any yield improvement can translate essentially directly into cost reduction. This application discloses a cleaving technique that can substantially increase the number of acceptable lasers that can be obtained from a given multilayer III/V semiconductor wafer. The novel technique is particularly advantageous in conjunction with vacuum cleaving and in situ facet passivation.
In semiconductor laser manufacture it is conventional to separate a completed wafer into a multiplicity of "bars" by a process that involves marking the cleavage plane with a scribe mark near the wafer edge, and causing fracture along the plane selected by the scribe mark by application of appropriate force. The thus created cleavage surfaces define the optical cavity of the lasers and should be of the highest quality. For obvious reasons, there should be minimal variation of cavity length from bar to bar. In practice a significant fraction of conventionally vacuum-cleaved surfaces have defects (e.g., striations), and/or are misplaced and thus do not yield lasers of the desired cavity length. Such cleavage errors are less of a problem if cleaving can be carried out in air, since commercially available cleaving apparatus can yield acceptable cleaving results. Cleaving in air however frequently results in chemical contamination of the cleavage surfaces and therefore is frequently undesirable.
After cleaving of the wafer into bars, a given (acceptable) bar is separated into individual lasers, and the lasers are then typically tested and packaged.
U.S. Pat. No. 4,237,601 discloses separating a wafer with thick substrate into bars by a process that involves etching deep channels into the back surface of the substrate of the multilayer wafer, followed by mechanical cleaving along the channels.
U.S. Pat. No. 4,689,125 discloses forming individual short laser chips by a process that involves electrochemically photoetching intersecting grooves into the back surface of the substrate, and cleaving along the grooves.
The prior art techniques have significant shortcomings and have, to the best of our knowledge, not been used in commercial laser production. For instance, both techniques involve etching continuous grooves into the wafer surface that is opposite to the surface that carries the features (e.g., patterned metalization) that define the location of individual lasers on the wafer. Alignment of the grooves to the features on the opposite surface is at best difficult and inconvenient.
In view of the importance of III/V semiconductor lasers, a method of making the lasers that includes a reliable and accurate cleaving technique, capable of implementation in vacuum, and capable of making with high yield lasers having essentially uniform cavity length, with mirror facets free from striations or other mechanical damage, would be highly desirable. This application discloses such a method.